Setting Yourself Up For Failure With Steam Cure

Overdriving A Steam Curing Of A Liner

“I did a couple of shots with my new system and cured it with steam. I was really impressed with how quickly I could cure the liner and was really impressed with the amount of steam my new unit was generating. The only glitch was the finished liner appearance. It had a waffled look to it. Not everywhere, but enough of it that I wondered why, but on the plus side, the guys had the liner cured in 40 minutes on a liner that was about 250′ long of 6” pipe, so I’m happy. To satisfy my curiosity, I thought I’d ask you if you had any reasons that I was seeing this kind of finish?”

Boiling Water with No Pressure

To answer your question, yep! is my best answer, I know why you observed the finish you saw. Let’s talk about the mechanics of steam. We all know that steam is made when water is boiled and transformed from a liquid to a gas. We also know that water boils at 212F at sea level. At elevations the boiling temperature decreases. At 7,500 feet the actual temperature is about 198F, so that will give you a range depending on the elevation you work in. We also know that steam under pressure actually increases the temperature of steam. For example, at 8 psi, steam temperature is actually producing 234F temperature. At 15 psi, the temperature at sea level is closer to 250F. So with those parameters, we can produce some serious temperatures when curing a liner.

Knowing those facts, we can now look at thermoset resins and how they cure at differing pressures and temperatures. You can look at the specifications sheet of the thermoset resins from any manufacturer and learn a lot about curing temperatures. Most will tell you to maintain a temperature at or below 200F. Why? Most manufacturers know that keeping temperatures below that will insure you don’t overdrive the forming of resin chains. When you overdrive the formation of the chemical chains that harden resin, you are forcing them to form too quickly. When they form too quickly, they bump into each other too quickly and stress crack. We all know what stress cracking does to resin in liners. They allow leaks and more importantly allow root intrusion.

Forming Resin Chains

Now that we know that part of the formation of the curing molecular process, we’ve set ourselves up for future failure when roots grow through your liner when we overheat the liner in the curing process. I’ve developed a specific protocol for curing liners with steam. It includes monitoring temperature during the curing process and maintaining a temperature around 180F. This temperature gives you a cushion while trying to maintain a temperature that won’t spike and cause stress cracking. It also gives you about the same amount of time to cure as 250F does without the risk of “over cooking” the liner.

If you’ve acquired a steam boiler, you should resolve to learn the correct method to insure you have a good liner with no stress cracking and no future failures caused from roots growing through the liner. Just so you know, I’ve experienced this issue in my past as we over cooked a liner in Southern California many years ago. A few years later, yes years, I was called to explain to a sewer district why the liner we installed had roots growing through the “impregnable” product we sold them years earlier. Embarrassing? Yes. Costly? Yes. A lot of customer repair work to let them continue CIPP lining in their agency? Yes. If you want to avoid my mistakes, heed my words. Follow your resin suppliers recommendations for curing temperatures and pressures. Acquire my guide for curing a liner with steam. You can get it by sending me an email: jheisler@pipeliningsupply.com. I will send it to you. One more thing. If your supplier tells you that their resin doesn’t work this way, you may want to find another supplier.

So what’s the prevention from over curing the liner? Keep temperatures during the cure at 180F +- and well below 212F. You do this by introducing more air and reducing steam volume when the resin is exotherming. With all of that said, steam curing a liner is a great way to cure liners, particularly larger diameter liners. But if you are looking for a failsafe method, hot water recirculating through the installed liner may give you less heartburn and is much easier to set and forget vs. the continue monitoring you should be doing with steam.

Don’t forget to see us in Dallas April 4 & 5 at the Fair Grounds for the WEQ Show. 

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